Largess with clear limits: in Africa and elsewhere, Gates Foundation takes focused approach to giving.

by Craig Timberg

KHAYELITSHA, South Africa — Bill and Melinda Gates came to the cramped tin shack of Nkosebaca Thingathinga one day this month to understand how the 61-year-old man had contracted tuberculosis — a major focus of research for the couple’s foundation — an astounding four times.